1. Field of the Invention
This invention relates to hydrophilic plastic materials useful as soft contact lenses, and more particularly relates to treatment of said hydrophilic soft contact lenses to make them more resistant to soiling in use.
2. The Prior Art
It has long been known to fabricate contact lenses from rigid materials such as glass and clear polymers, e.g., essentially hydrophobic acrylic-type polymers as polymethylmethacrylate and the like. Although more safely handled and used than glass, such hydrophobic polymer materials have been only moderately successful as contact lenses, being too hard and uncomfortable to the wearer. More recently, contact lens compositions have been developed from hydrophilic-type polymers which are softer and generally more easily accommodated by the eye. Thus, the use of hydrophilic polymer lens compositions is becoming of increasing importance in ophthalmological practice.
Hydrophilic polymers useful as soft contact lenses typically are lightly cross-linked copolymers derived from one or more hydroxyl-group containing monomers. In their hydrated state, these polymers are known generally in the art as "hydrogels". Hydrogels are specifically defined as coherent, three-dimensional polymer structures or networks which have the ability to absorb or imbibe large quantities of water without dissolution. At the present time, the specific class of polymer hydrogels which have gained particular commercial acceptance as soft contact lenses are those derived from acrylic esters. U.S. Pat. Nos. 2,976,576 and 3,220,960, issued to O. Wichterle and D. Lim on Mar. 28, 1961 and on Nov. 30, 1965, respectively, are early patents which describe the use of acrylic ester hydrogels for the manufacture of soft contact lenses. Many subsequent patents as well as other technical articles are directed to the preparation of numerous other acrylic ester-type hydrogels which differ primarily in the type and/or percentage of comonomers contained therein.
In the main, acrylic ester hydrogels are all derived by copolymerizing a major amount of a water-soluble monoester of acrylic or methacrylic acid in which the ester moiety contains at least one hydrophilic group and a minor amount of a bifunctional diester of acrylic or methacrylic acid which cross links the hydrophilic group-containing monomer as it polymerizes.
Although presently used contact lenses fabricated from polymer hydrogels are much softer than the prior hard contact lenses and can be accommodated by the wearer with relatively little discomfort, they nevertheless have disadvantageous properties and likewise have not been completely satisfactory.
A major problem with hydrophilic soft contact lenses is the deposition of various soils contained in the tears on the surface of the lens. This invention relates to methods of treating the surfaces of hydrophilic contact lenses while they are in their dehydrated or dry state. The treatment described reduced the amount of soiling of the lenses by varying degrees, in particular, the rate of lysozyme deposition on the hydrated lenses is reduced significantly. A description of the problem with the soiling of hydrophilic or soft contact lenses is contained in an article titled "Analysis of Deposits on High Water Content Contact Lenses" from the J. of Biomedicals Materials Research, Vol. 17, pp. 261 through 274, 1983.
It is an object of this invention, therefore, to provide a soft contact lens which is resistant to soiling by deposits contained in tears of the human eye.
This and other objects of this invention will become apparent to those skilled in the art from the description of the invention which follows.